The present invention concerns a drive train, in particular for a motor vehicle, in which the heat flow generated by a drive motor is used for evaporating a working fluid and the evaporated working fluid is expanded in a steam engine, to generate an additional drive power.
Drive units of the type above mentioned have been known to the man of the art for many decades, and have been hardly further developed in the meantime. Due to today's harsher requirements in terms of optimal energy consumption of vehicles driven by internal combustion engine, in particular rail vehicles or lorries, such drive units have recently aroused the interest of the trade. In this context, different embodiments have been suggested, in which the waste heat is used at different positions of the drive train for steam generation, for instance in the exhaust gas stream, in the so-called exhaust gas recirculation of an internal combustion engine or in the cooling circuit. We refer here for instance to the international patent application WO 2004/033859 A1.
Although basic approaches are available for maximum waste heat recycling, there is a continuous need for further improvements so as to optimise waste heat recycling, hereby to lower the fuel consumption and/or to increase the power of the drive motor, however to simultaneously meet the stringent requirements in terms of future exhaust gas emissions.
Disclosure DE 31 48 208 A1 describes a drive device composed of internal combustion engine and steam engine, in which the steam engine is operated by a separate water/steam circuit, which is coupled to the cooling water system of the internal combustion engine via a first heat exchanger and which is guided via a heat exchanger acting as an evaporator, through which the exhaust gas of the internal combustion engine is guided. The steam generation in the exhaust gas can be adjusted by means of a controlled pump by means of which the amount of water injected into the exhaust gas heat exchanger can be dosed.
EP 1 249 580 A1 describes a heat recovery system for an internal combustion engine having a plurality of evaporators, which work at different temperature levels.